As for the hinged fin: the 707 had the same feature and I'd be surprised of he 737 didn't have it too. I once saw a Monarch 720 outside their old black hangar at Luton, (northernmost corner of the apron, besides the Britannia ops block. Both gone now I believe) the 720's fin was folded flat on top of the right hand stabiliser in order to get it in the hangar.
Were the hangars just too small to simply build a doghouse over the middle of the top of the doors?
and is it true that the reason the Constellation had three fins is to reduce the height so that it could fit inside the existing hangars?